Physical Sciences and Mathematics Commons^™

The 'Quantal Newtonian' First Law: A Complementary Perspective To The Stationary-State Quantum Theory Of Electrons, Viraht Sahni

Publications and Research

A complementary perspective to the Göttingen-Copenhagen interpretation of stationary-state quantum theory of electrons in an electromagnetic field is described. The perspective, derived from Schrödinger-Pauli theory, is that of the individual electron via its equation of motion or ‘Quantal Newtonian’ First Law. The Law is in terms of ‘classical’ fields experienced by each electron: the sum of the external and internal fields vanishes. The external field is a sum of the electrostatic and Lorentz fields. The internal field is a sum of fields’ representative of Pauli and Coulomb correlations; kinetic effects; electron density; and internal magnetic component. The energy is obtained …

Studying Electron Dynamics For Quantum Materials With Real Space Resolution: A Wannier Orbital Approach To Spectroscopy Using High-Performance Supercomputers, Casey J. Eichstaedt

Doctoral Dissertations

Quantum materials have a promising future for energy and security applications which will lay the bedrock for material science research for decades to follow. Partic- ularly, ‘one-dimensional’ Mott-insulating cuprates such as SrCuO 2 and (Ca)Sr 2 CuO 3 have been deemed to fall under a ‘fractionalization’ paradigm in which the electrons disintegrate into bosonic collective excitations of their fundamental constituents— spin, charge, and ‘orbital’ degrees of freedom— due to the anisotropic crystalline structure, deeming them outside the band theory of solids. Here, I provide ab initio theory for the ‘one-dimensional’ cuprates SrCuO 2 and (Ca)Sr 2 CuO 3 using no …

Data-Driven Approaches To Complex Materials: Applications To Amorphous Solids, Dil Kumar Limbu

Dissertations

While conventional approaches to materials modeling made significant contributions and advanced our understanding of materials properties in the past decades, these approaches often cannot be applied to disordered materials (e.g., glasses) for which accurate total-energy functionals or forces are either not available or it is infeasible to employ due to computational complexities associated with modeling disordered solids in the absence of translational symmetry. In this dissertation, a number of information-driven probabilistic methods were developed for the structural determination of a range of materials including disordered solids to transition metal clusters. The ground-state structures of transition-metal clusters of iron, nickel, and …

Disorder By Design: A Data-Driven Approach To Amorphous Semiconductors Without Total-Energy Functionals, Dil K. Limbu, Stephen R. Elliott, Raymond Atta-Fynn, Parthapratim Biswas

Faculty Publications

X-ray diffraction, Amorphous silicon, Multi-objective optimization, Monte Carlo methods. This paper addresses a difficult inverse problem that involves the reconstruction of a three-dimensional model of tetrahedral amorphous semiconductors via inversion of diffraction data. By posing the material-structure determination as a multiobjective optimization program, it has been shown that the problem can be solved accurately using a few structural constraints, but no total-energy functionals/forces, which describe the local chemistry of amorphous networks. The approach yields highly realistic models of amorphous silicon, with no or only a few coordination defects (≤1%), a narrow bond-angle distribution of width 9–11.5°, and an electronic gap …

Symmetry And Interface Considerations For Interactions On Mos2, Prescott E. Evans

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

The critical role of symmetry, in adsorbate-MoS₂ interactions, has been demonstrated through a variety of electronic structure, topology, and catalytic studies of MoS₂ and MoS₂ composites.A combination of density functional theory and experiment exhibiting diiodobenzene isomer dependent adsorption rates highlight frontier orbital symmetry as key to adsorption on MoS₂. It is clear that the geometry and symmetry of MoS₂ influences the creation and stability of surface defects, that in turn affect catalytic activity and a myriad of other applications. We have shown that surface reactions such the methanol to methoxy reaction can create defects …

Magnetic Borophenes From An Evolutionary Search, Meng-Hong Zhu, Xiao-Ji Weng, Guoying Gao, Shuai Dong, Ling-Fang Lin, Wei-Hua Wang, Qiang Zhu, Artem R. Oganov, Xiao Dong, Yongjun Tian, Xiang-Feng Zhou, Hui-Tian Wang

Physics & Astronomy Faculty Research

A computational methodology based on ab initio evolutionary algorithms and spin-polarized density functional theory was developed to predict two-dimensional magnetic materials. Its application to a model system borophene reveals an unexpected rich magnetism and polymorphism. A metastable borophene with nonzero thickness is an antiferromagnetic semiconductor from first-principles calculations, and can be further tuned into a half-metal by finite electron doping. In this borophene, the buckling and coupling among three atomic layers are not only responsible for magnetism, but also result in an out-of-plane negative Poisson's ratio under uniaxial tension, making it the first elemental material possessing auxetic and magnetic properties …

High Resolution Near-Infrared/Visible Intracavity Laser Spectroscopy Of Small Molecules, Jack Harms

Dissertations

Intracavity laser spectroscopy has been used to study the electronic structure of several small molecules. The molecules studied as part of this dissertation include germanium hydride (GeH), copper oxide (CuO), nickel chloride (NiCl), platinum fluoride (PtF), platinum chloride (PtCl), and copper hydroxide (CuOH). This work encompasses five peer-reviewed publications and two submitted manuscripts.

Ab Initio Study Of Li2 Cata2 O7 Compound: Electronic And Optical Properties Forthree Phases, Murat Ayci̇bi̇n

Turkish Journal of Physics

The Li2 CaTa2 O7 compound belongs to the Ruddlesden-Popper family of layered perovskites. First principle approximation was used to investigate the electronic band structure and optical properties of the compound for three phases. Independent of the studied compound's structural type, Li2 CaTa2 O7 has semiconductor behavior and direct transition. In addition, the forbidden energy band gap of the compound decreases with rising temperature, as expected. Furthermore, the 3d orbital of Ca contributes to the conduction band due to the crystal field effect. Moreover, the optical response of the chosen axes of the compound to incoming electromagnetic rays varies with phase …

Pressure-Induced Structural Phase Transition And Electronic Structure Of In$_{1-X}$Ga$_{X}$P Alloys: A Dft Study, Kabita Khoirom, Indrajit Sharma, Brojen Singh, Ramkumar Thapa

Turkish Journal of Physics

We present the density functional calculation to study the pressure-induced structural phase transition and electronic structure of In$_{1-x}$Ga$_{x}$P ($x =$ 0.0, 0.25, 0.5, 0.75, 1) alloys. We report the optimized structural parameters such as lattice constant, bulk modulus, and derivative of the bulk modulus of the alloys. Our calculation confirms that the alloys in the zinc-blende structure are more stable than in the rock-salt structure. The phase transition study from zinc-blende to rock-salt under pressure shows that the transition pressure increases with an increase in doping concentration. The energy band diagram of the alloys in the zinc-blende phase reveals a …

Real-Time Observation Of Molecular Spinning With Angular High-Harmonic Spectroscopy, Lixin He, Pengfei Lan, Anh-Thu Le, Baoning Wang, Bincheng Wang, Xiaosong Zhu, Peixiang Lu, C. D. Lin

Physics Faculty Research & Creative Works

We demonstrate an angular high-harmonic spectroscopy method to probe the spinning dynamics of a molecular rotation wave packet in real time. With the excitation of two time-delayed, polarization-skewed pump pulses, the molecular ensemble is impulsively kicked to rotate unidirectionally, which is subsequently irradiated by another delayed probe pulse for high-order harmonic generation (HHG). The spatiotemporal evolution of the molecular rotation wave packet is visualized from the time-dependent angular distributions of the HHG yields and frequency shift measured at various polarization directions and time delays of the probe pulse. The observed frequency shift in HHG is demonstrated to arise from the …

Electronic And Optical Properties Of La-Doped Sr3Ir2O7 Epitaxial Thin Films, Maryam Souri, Jsaminka Terzic, J. M. Johnson, John G. Connell, John H. Gruenewald, J. Thompson, Joseph W. Brill, J. Hwang, Gang Cao, Sung S. Ambrose Seo

Physics and Astronomy Faculty Publications

We have investigated structural, transport, and optical properties of tensile strained (Sr_1−xLa_x)₃Ir₂O₇ (x = 0, 0.025, 0.05) epitaxial thin films. While high-T_c superconductivity is predicted theoretically in the system, we have observed that all of the samples remain insulating with finite optical gap energies and Mott variable-range hopping characteristics in transport. Cross-sectional scanning transmission electron microscopy indicates that structural defects such as stacking faults appear in this system. The insulating behavior of the La-doped Sr₃Ir₂O₇ thin films is presumably due to disorder-induced …

Semiconductor Color-Center Structure And Excitation Spectra: Equation-Of-Motion Coupled-Cluster Description Of Vacancy And Transition-Metal Defect Photoluminescence, Jesse J. Lutz, Xiaofeng F. Duan, Larry W. Burggraf

Faculty Publications

Valence excitation spectra are computed for deep-center silicon-vacancy defects in 3C, 4H, and 6H silicon carbide (SiC), and comparisons are made with literature photoluminescence measurements. Optimizations of nuclear geometries surrounding the defect centers are performed within a Gaussian basis-set framework using many-body perturbation theory or density functional theory (DFT) methods, with computational expenses minimized by a QM/MM technique called SIMOMM. Vertical excitation energies are subsequently obtained by applying excitation-energy, electron-attached, and ionized equation-of-motion coupled-cluster (EOMCC) methods, where appropriate, as well as time-dependent (TD) DFT, to small models including only a few atoms adjacent to the defect center. We consider the …

Electronic Structure And Direct Observation Of Ferrimagnetism In Multiferroic Hexagonal Ybfeo3, Shi Cao, Kishan Sinha, Xin Zhang, Xiaozhe Zhang, Xiao Wang, Yuewei Yin, Alpha T. N’Diaye, Jian Wang, David J. Keavney, Tula R. Paudel, Yaohua Liu, Xuemei Cheng, Evgeny Y. Tsymbal, Peter A. Dowben, Xiaoshan Xu

Evgeny Tsymbal Publications

The magnetic interactions between rare-earth and Fe ions in hexagonal rare-earth ferrites (h-RFeO₃), may amplify the weak ferromagnetic moment on Fe, making these materials more appealing as multiferroics. To elucidate the interaction strength between the rare-earth and Fe ions as well as the magnetic moment of the rare-earth ions, element-specific magnetic characterization is needed. Using x-ray magnetic circular dichroism, we have studied the ferrimagnetism in h-YbFeO₃ by measuring the magnetization of Fe and Yb separately. The results directly show antialignment of magnetization of Yb and Fe ions in h-YbFeO₃ at low temperature, …

Optical Signatures Of Spin-Orbit Exciton In Bandwidth-Controlled Sr2Iro4 Epitaxial Films Via High-Concentration Ca And Ba Doping, Maryam Souri, B. H. Kim, John H. Gruenewald, John G. Connell, J. Thompson, J. Nichols, Jsaminka Terzic, B. I. Min, Gang Cao, Joseph W. Brill, Sung S. Ambrose Seo

Physics and Astronomy Faculty Publications

We have investigated the electronic and optical properties of (Sr_1−xCa_x)₂IrO₄ (x = 0–0.375) and (Sr_1−yBa_y)₂IrO₄ (y = 0–0.375) epitaxial thin films, in which the bandwidth is systematically tuned via chemical substitutions of Sr ions by Ca and Ba. Transport measurements indicate that the thin-film series exhibits insulating behavior, similar to the J_eff = 1/2 spin-orbit Mott insulator Sr₂IrO₄. As the average A-site ionic radius increases from (Sr_1−xCa_x)₂IrO₄ to (Sr …

Tunable Magnetism In Metal Adsorbed Fluorinated Nanoporous Graphene, Pankaj Kumar, Vinit Sharma, Fernando A. Reboredo, Li-Ming Yang, Raghani Pushpa

Physics Faculty Publications and Presentations

Developing nanostructures with tunable magnetic states is crucial for designing novel data storage and quantum information devices. Using density functional theory, we investigate the thermodynamic stability and magnetic properties of tungsten adsorbed tri-vacancy fluorinated (TVF) graphene. We demonstrate a strong structure-property relationship and its response to external stimuli via defect engineering in graphene-based materials. Complex interplay between defect states and the chemisorbed atom results in a large magnetic moment of 7 μ_B along with high in-plane magneto-crystalline anisotropy energy (MAE) of 17 meV. Under the influence of electric field, spin crossover effect accompanied by a change in the MAE …

Communication: Visualization And Spectroscopy Of Defects Induced By Dehydrogenation In Individual Silicon Nanocrystals, Dmitry A. Kislitsyn, Jon M. Mills, Vancho Kocevski, Sheng-Kuei Chiu, William J.I. Debenedetti, Christian F. Gervasi, Benjamen N. Taber, Ariel E. Rosenfield, Olle Eriksson, Ján Rusz, Andrea Mitchell Goforth, George V. Nazin

Chemistry Faculty Publications and Presentations

We present results of a scanning tunneling spectroscopy (STS) study of the impact of dehydrogenation on the electronic structures of hydrogen-passivated silicon nanocrystals (SiNCs) supported on the Au(111)surface. Gradual dehydrogenation is achieved by injecting high-energy electrons into individual SiNCs, which results, initially, in reduction of the electronic bandgap, and eventually produces midgap electronic states. We use theoretical calculations to show that the STS spectra of midgap states are consistent with the presence of silicon dangling bonds, which are found in different charge states. Our calculations also suggest that the observed initial reduction of the electronic bandgap is attributable to the …

Hallmarks Of The Mott-Metal Crossover In The Hole-Doped Pseudospin-1/2 Mott Insulator Sr2Iro4, Yue Cao, Qiang Wang, Justin A. Waugh, Theodore J. Reber, Haoxiang Li, Xiaoqing Zhou, Stephen Parham, S. -R. Park, Nicholas C. Plumb, Eli Rotenberg, Aaron Bostwick, Jonathan D. Denlinger, Tongfei Qi, Michael A. Hermele, Gang Cao, Daniel S. Dessau

Physics and Astronomy Faculty Publications

The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr₂IrO₄. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observed …

On The Structural Origin Of The Single-Ion Magnetic Anisotropy In Lufeo3, Shi Cao, Xiaozhe Zhang, Tula R. Paudel, Kishan Sinha, Xiao Wang, Xuanyuan Jiang, Wenbin Wang, Stuart Brutsche, Jian Wang, Philip J. Ryan, Jong-Woo Kim, Xuemei Cheng, Evgeny Y. Tsymbal, Peter A. Dowben, Xiaoshan Xu

Evgeny Tsymbal Publications

Electronic structures for the conduction bands of both hexagonal and orthorhombic LuFeO₃ thin films have been measured using x-ray absorption spectroscopy at oxygen K (O K) edge. Dramatic differences in both the spectra shape and the linear dichroism are observed. These differences in the spectra can be explained using the differences in crystal field splitting of the metal (Fe and Lu) electronic states and the differences in O 2p-Fe 3d and O 2p-Lu 5d hybridizations. While the oxidation states has not changed, the spectra are sensitive to the changes in the local environments of the Fe³⁺ and Lu …

Mapping Of Defects In Individual Silicon Nanocrystals Using Real- Space Spectroscopy, Dmitry A. Kislitsyn, Vancho Kocevski, Jon M. Mills, Sheng-Kuei Chiu, Christian F. Gervasi, Benjamen N. Taber, Ariel E. Rosenfield, Olle Eriksson, Ján Rusz, Andrea Mitchell Goforth, George V. Nazin

Chemistry Faculty Publications and Presentations

The photophysical properties of silicon semiconductor nanocrystals (SiNCs) are extremely sensitive to the presence of surface chemical defects, many of which are easily produced by oxidation under ambient conditions. The diversity of chemical structures of such defects and the lack of tools capable of probing individual defects continue to impede understanding of the roles of these defects in SiNC photophysics. We use scanning tunneling spectroscopy to study the impact of surface defects on the electronic structures of hydrogen-passivated SiNCs supported on the Au(111) surface. Spatial maps of the local electronic density of states (LDOS) produced by our measurements allowed us …

Scalability Improvements To Nrlmol For Dft Calculations Of Large Molecules, Carlos Manuel Diaz

Open Access Theses & Dissertations

Advances in high performance computing (HPC) have provided a way to treat large, computationally demanding tasks using thousands of processors. With the development of more powerful HPC architectures, the need to create efficient and scalable code has grown more important. Electronic structure calculations are valuable in understanding experimental observations and are routinely used for new materials predictions. For the electronic structure calculations, the memory and computation time are proportional to the number of atoms. Memory requirements for these calculations scale as N2, where N is the number of atoms. While the recent advances in HPC offer platforms with large numbers …

Electronic Structures Of Lanthanum, Samarium, And Gadolinium Sulfides, Lu Wang, Chris M. Marin, Wai-Ning Mei, Chin Li Cheung

Physics Faculty Publications

In this study, we report our efforts to elucidate the electronic structures of two lattice structures of lanthanide sulfides (LnS and Ln3S4) and for three lanthanides (Ln = La, Sm and Gd) using density functional theory calculations performed with the CASTEP code. A DFT+U method was used for the corrections of on-site Coulomb interactions with U = 6 eV. The calculated electronic structures show that both lanthanum and gadolinium sulfides have metallic properties, consistent with the available experimental results. However, the calculated electronic structure of Sm3S4 is considerably different from those of the La3S4 and Gd3S4 and is predicted to …

Boron Nitride Nanotubes For Spintronics, Kamal B. Dhungana, Ranjit Pati

Department of Physics Publications

With the end of Moore's law in sight, researchers are in search of an alternative approach to manipulate information. Spintronics or spin-based electronics, which uses the spin state of electrons to store, process and communicate information, offers exciting opportunities to sustain the current growth in the information industry. For example, the discovery of the giant magneto resistance (GMR) effect, which provides the foundation behind modern high density data storage devices, is an important success story of spintronics; GMR-based sensors have wide applications, ranging from automotive industry to biology. In recent years, with the tremendous progress in nanotechnology, spintronics has crossed …

Enhancing The Insulation Of Wide-Range Spectrum In The Pva/N Thin Film By Doping Zno Nanowires, Yu-Chen Lin, Ching-Hsiang Vhen, Liang-Yih Chen, Shih-Chieh Hsu, Shizhi Qian

Mechanical & Aerospace Engineering Faculty Publications

In this study, polyvinyl alcohol/nitrogen (PVA/N) hybrid thin films doped with sharp-sword ZnO nanowires with insulating effect and wide-range spectrum are demonstrated for the first time. PVA/N doped ZnO nanocomposites were developed by blending PVA and N-doped ZnO nanowires in water at room temperature. Measurements from the field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman, and photoluminescence emission (PL) spectra of the products show that nitrogen is successfully doped into the ZnO wurtzite crystal lattice. In addition, the refractive index of PVA/N doped ZnO hybrid thin films can be controlled by varying the doped ZnO nanowires under different …

Modeling The Atomic And Electronic Structure Of Metal-Metal, Metal-Semiconductor And Semiconductor-Oxide Interfaces, Ganesh Krishna Hegde

Open Access Dissertations

The continuous downward scaling of electronic devices has renewed attention on the importance of the role of material interfaces in the functioning of key components in electronic technology in recent times. It has also brought into focus the utility of

atomistic modeling in providing insights from a materials design perspective. In this thesis, a combination of Semi Empirical Tight-Binding (TB), first-principles Density

Functional Theory and Reactive Molecular Dynamics (MD) modeling is used to study aspects of the electronic and atomic structure of three such 'canonical' material interfaces - Metal-Metal, Metal-Semiconductor and Semiconductor oxide interfaces.

An important contribution of this thesis …

Tuning Electronic Structure Via Exipatial Strain In Sr2Iro4 Thin Films, J. Nichols, Jsaminka Terzic, Emily Geraldine Bittle, Oleksandr B. Korneta, Lance E. De Long, Joseph Brill, Gang Cao, Sung S. Ambrose Seo

Physics and Astronomy Faculty Publications

We have synthesized epitaxial Sr₂IrO₄ thin-films on various substrates and studied their electronic structure as a function of lattice-strain. Under tensile (compressive) strain, increased (decreased) Ir-O-Ir bond-angle is expected to result in increased (decreased) electronic bandwidth. However, we have observed that the two optical absorption peaks near 0.5 eV and 1.0 eV are shifted to higher (lower) energies under tensile (compressive) strain, indicating that the electronic-correlation energy is also affected by in-plane lattice-strain. The effective tuning of electronic structure under lattice-modification provides an important insight into the physics driven by the coexisting strong spin-orbit coupling and electronic …

A Non-Linear Eigensolver-Based Alternative To Traditional Self-Consistent Electronic Structure Calculation Methods, Brendan E. Gavin

Masters Theses 1911 - February 2014

This thesis presents a means of enhancing the iterative calculation techniques used in electronic structure calculations, particularly Kohn-Sham DFT. Based on the subspace iteration method of the FEAST eigenvalue solving algorithm, this nonlinear FEAST algorithm (NLFEAST) improves the convergence rate of traditional iterative methods and dramatically improves their robustness. A description of the algorithm is given, along with the results of numerical experiments that demonstrate its effectiveness and offer insight into the factors that determine how well it performs.

Angular And Dynamical Properties In Resonant Inelastic X-Ray Scattering: Case Study Of Chlorine-Containing Molecules, Renaud Guillemin, Wayne C. Stolte, Loic Journel, Stephane Carniato, Maria Novella Piancastelli, Dennis W. Lindle, Marc Simon

Chemistry and Biochemistry Faculty Research

Polarization-dependent resonant inelastic x-ray scattering (RIXS) has been shown to be a probe of molecular-field effects on the electronic structure of isolated molecules. In this experimental analysis we explain the linear dichroism observed in Cl 2p polarized RIXS following Cl 1s excitation of a series of chlorofluoromethanes (CF3Cl, CF2Cl2, CFCl3, and CCl4) as due to molecular-field effects, including singlet-triplet exchange. We present an approach to extract directly the 2p inner-shell electronic state populations from the experimental measurements. Using the angular properties of the measured KV emission we also are able to determine the value of the polarization anisotropy parameter βp …

Mott Transition And Electronic Structure In Complex Oxide Heterostructures, Jian Liu

Graduate Theses and Dissertations

Strongly correlated electron systems, particularly transition metal oxides, have been a focus of condensed matter physics for more than two decades since the discovery of high-temperature superconducting cuprates. Diverse competing phases emerge, spanning from exotic magnetism to unconventional superconductivity, in proximity to the localized-itinerant transition of Mott insulators. While studies were concentrated on bulk crystals, the recent rapid advance in synthesis has enabled fabrication of high-quality oxide heterostructures, offering a new route to create novel artificial quantum materials.

This dissertation details the investigation on ultrathin films and heterostructures of 3d⁷(t_2g⁶e_g¹) systems with …

Fermi Surface, Ground-State Electronic Structure, And Positron Experiments In Yba₂Cu₃O₇, A. Bansil, R. Pankaluoto, R. S. Rao, P. E. Mijnarends, W. Dlugosz, R. Prasad, L. C. Smedskjaer

Arun Bansil

We present calculations of electron-positron momentum density in YBa₂Cu₃O₇ based on band theory in the local-density approximation. Theoretical predictions are in semiquantitative accord with the corresponding two-dimensional positron-annihilation angular-correlation measurements. These results indicate that the conventional local-density-approximation band-theory picture provides a reasonable description of the ground-state electronic structure and the Fermi surface of YBa₂Cu₃O₇. Several Fermi-surface-related features are suggested in the positron spectra for the first time.

Electronic Structure Of Au70pd30 Disordered Alloy, E. Arola, C. J. Barnes, R. S. Rao, A. Bansil

Arun Bansil

We present angle-resolved photoemission (normal-emission) measurements from the (100) surface of a disordered Au₇₀Pd₃₀ alloy single crystal using He i, Ne i, He ii, and Ne ii excitations. The experimental results are interpreted via fully relativistic Korringa-Kohn-Rostoker coherent-potential-approximation computations of complex-energy bands, spectral densities, and total and site-decomposed densities of states in the alloy. Our measurements and calculations indicate that the main effects of adding Pd to Au are the following: (i) the appearance of a Pd-derived d-band complex with small dispersion, distinctly above the Au d-band edge, centered about 1 eV below the Fermi energy, (ii) the Au-derived d-band …